1. Field of the Invention
This invention relates generally to semiconductor laser assemblies, and more particularly to semiconductor lasers that hermetically sealed with a seal cap.
2. Description of Related Art
A variety of devices are formed on wafers including but not limited to lasers, photodetectors, filters electronic circuits and MEMs. These devices are formed on the wafers utilizing a variety of standard multi-processing steps and procedures. The wafer is typically moved from one process station to another until the final device is completed on the wafer. The devices are then tested. Following testing, the wafer is diced and individual devices are then mounted, electrical connections are made and then there is a final sealing.
This type of wafer scale manufacturing exposes the individual devices to contaminants and corrosive elements found in the atmosphere because of the lengthy time it takes to complete the manufacturing process. Corrosive elements, such as moisture and oxygen, can cause a degradation in the device that is made.
Laser diodes typically include an n-type substrate, an active layer, a p-type clad layer and a p-type cap layer that is laminated over the n-type substrate. In one such semiconductor laser, the n-type substrate is formed of AlGaAs and the active layer is formed of GaAs. An electrode is selectively formed on the obverse surface of the laser diode in an opening of the p-type cap layer. A rear electrode is formed on the reverse surface of the substrate. The resulting structure is a laser diode chip more commonly known as a double heterostructure (DH structure). This laser diode chip can be mounted on a radiation plate. The assembly is then encapsulated to hermetically seal the device. Different methods of encapsulation include the use of metal packages or caps with a light transmitting window, lenses or optical fibers. Wafer scale encapsulation is used on low power light emitting devices where the devices are typically encapsulated with an encapsulating resin layer typically formed of a transparent epoxy resin or the like.
Because the epoxy resin abuts directly against a light-emitting end face of the laser diode from which an output beam is emitted, the resin can become decomposed due to the heat from the output beam. As the degradation increases, the light emission efficiency of the laser diode declines. In some cases, the promoted decomposition results in the formation of a cavity in the encapsulating resin layer in the vicinity of the light-emitting end face.
In one diode laser chip, the output beam has a power 5 mW and an oscillation wavelength of 780 nm is continuously oscillated in a state close to its maximum rating. A conical broken area with a bottom diameter is formed in the encapsulating resin layer in the vicinity of the light-emitting end face after about 1000 hours of operation. Additionally, the encapsulating resins layer often melts and breaks.
There is a need for improvement in wafer scale manufacturing processes and procedures along with the resultant devices that are created. There is a further need to seal the individual devices on the wafer before corrosive environment elements create a degradation.